Saponins, glycosides widely distributed in the plant kingdom, include diverse ring compounds formed by the non-sugar portion. A saponin, contained in ginseng or red ginseng as a major physiologically active ingredient, is called ginsenoside which means ginseng glycoside, named to distinguish it from other vegetables' saponin based on it's different chemical structure.
Ginsenosides are classified into three groups based on their aglycone structure: Protopanaxadiol (PPD)-type ginsenosides, Protopanaxatriol (PPT)-type ginsenosides, and Oleanolic acid-type ginsenosides. These three groups are further classified based on the position and number of sugar moieties (aglycones) attached by a glycosidic bond at C-3, C-6, and C-20 positions of the rings in the chemical structure. Among them, Rg1, Re, Rb1, Rc and Rb2 are major ginsenosides that account for over 90% of total ginsenoside content (Park, 2004), but show a very low in vivo absorption when orally administered into the human body, because of their large size. Therefore, deglycosylation of major ginsenosides is required in order to show effective physiological activities in vivo (Tawab et al., 2003; Akao et al., 1998).
In recent decades, excellent pharmacological effects of minor ginsenosides such as Rg3, Rh2 and compound K have been revealed. These recent studies have brought more attention to minor ginsenosides having superior pharmacological effects, such as F2, Rg3, Rh1, Rh2, and compound K (C—K), and there is a need to develop a method for increasing the content ratio of particular minor ginsenosides.
Among them, the protopanaxadiol-type ginsenosides, Rh1 and Rh2 are reported to strongly induce the differentiation of F9 teratocarcinoma stem cells (F9 teratocarcinoma) (Lee et al., Proc. 6th, Intl. Ginseng symp., 127, 1993), and they are also reported to show strong inhibitory effects on the proliferation of various tumor cells such as B16 melanoma, MK-1 (stomach cancer cell) (Matsunaga et al., Chem, Pharm. Bull., 38, 3480, 1990) and ovarian cancer cell (HRA) (Kikuchi et al., Anticancer Drugs. England., 2, 63, 1991). Rh2 has such excellent pharmacological effects, but is present in red ginseng in only trace amounts. Even though methods for the mass-production of Rh2 have been actively studied, effective methods have not been established yet.
Regarding the ginsenoside F2, F2 has been known as an ingredient having the effects of suppressing the proliferation of tumor cells and reversing multi-drug resistance in tumor cells and bacteria (Sung et al., Korean Journal of Pharmacognosy 28(1), 35, 1997). It is known that ginseng saponins are metabolized by intestinal flora such as Prevotellaris after they are orally administered, and their metabolite F2 shows pharmaceutical effects. However, useful F2 is also present only in small amounts in some ginsengs, and thus it is difficult to produce a large amount thereof. In addition, it is difficult to produce only high-purity F2 because of the production of various secondary metabolites during the metabolic process.
For the production of minor ginsenosides that are present in a small amount, chemical decomposition (De Mayo et al., canad. J. Chem., 43, 2033, 1965), enzymatic method (Kitagawa et al., Terahedron Letters, 30, 2283, 1974), and glycoside synthesis (Korean Patent No. 10-2005-0007250) have been suggested, but these methods have limitations on mass-production such as 1) the many production steps required for the production process, 2) the loss of desired compounds during processing, 3) the use of inedible catalysts, or 4) low yield.
In particular, enzymes such as ginsenoside glycosidase, α-L-arabinopyranosidase, α-L-arabinofuranosidase, and α-L-rhamnosidase can be used in the enzymatic method, and there have been many studies on the biotransformation of major ginsenosides such Rb1, Rb2, Rc, and Re using these enzymes. However, these methods are also ineffective for mass-production, and have a problem of high production costs.
Moreover, not all enzymes of β-glucosidase, α-L-arabinopyranosidase, α-L-arabinofuranosidase, and α-L-rhamnosidase have the activity of biotransformation of major ginsenosides into minor ginsenosides. For example, the present inventors demonstrated that beta-glucosidase known to be derived from Arthrobacter chlorophenolicus A6 has no activity of the biotransformation of ginsenoside. In addition, even though a known enzyme, for example, beta-glucosidase A, has biotransformation activity into Rb1, the activity was not satisfactory.
Further, Korean Patent Application No. 10-1999-0045180 provides a method for preparing ginsenoside Rh2 by degradation of saccharide of PPD-type ginsenoside using saponin alpha-glucosidase. The saponin alpha-glucosidase of the above invention converts ginsenoside Rd into ginsenoside Rh2 via ginsenoside F2. In addition, ginsenoside Rh2 can be produced from ginsenoside Rb1 and Rc. As described in Example 3, however, the saponin alpha-glucosidase should be obtained by removal of bacterial cells from the culture broth of Aspergillus in media containing wheat bran and ginseng powder. Thus, the low production yield increases the production cost in mass-production, and loss of the desired product problematically occurs during the production process.